CN114797864B - Preparation method for small-diameter bulk single-walled carbon nanotube growth catalyst - Google Patents

Abstract

The invention provides a catalyst for growing small-diameter bulk single-walled carbon nanotubes, a preparation method thereof and a preparation method of the small-diameter bulk single-walled carbon nanotubes. The catalyst provided by the invention uses the complexing agent to effectively limit the size of metal catalyst particles, the catalyst carrier is easy to remove, the subsequent application of the carbon nano tube is convenient, the working procedure is simple, and the prepared carbon nano tube has smaller diameter and narrower tube diameter distribution.

Description

Preparation method for small-diameter bulk single-walled carbon nanotube growth catalyst

Technical field

The invention relates to a method for preparing a carbon material growth catalyst, and in particular to a method for preparing a small-diameter bulk single-wall carbon nanotube growth catalyst.

Background technique

The structurally controllable growth of single-walled carbon nanotubes is a key challenge faced in high-end applications such as quantum devices, bioimaging, electronics, and optoelectronics. The band gap width of semiconducting single-walled carbon nanotubes is directly related to the diameter of the tube. By controlling the diameter of single-walled carbon nanotubes, the band gap can be adjusted to meet the requirements of corresponding applications. For example, for near-infrared biofluorescence imaging, single-walled carbon nanotubes with a diameter of 0.8-1.2 nm can emit fluorescence in the near-infrared 2 zone window of biological tissues. For single-photon light sources in quantum devices, single-walled carbon nanotubes with a diameter of 0.9-1.2nm have a suitable emission wavelength. In single-walled carbon nanotube film field effect transistors, the size and uniformity of the carbon nanotube band gap will directly affect device performance. In single-walled carbon nanotube-fullerene solar cells, the internal quantum efficiency of the cell decreases as the diameter of the carbon nanotube increases, which means that only small-diameter carbon nanotubes are suitable for use in this type of solar cell. middle. At the same time, small-diameter bulk carbon nanotubes are easier to disperse in solution, so they are more suitable for separating carbon nanotubes with different conductivities and chiral indices through solution phase separation.

In the process of growing single-walled carbon nanotubes by chemical vapor deposition (CVD), there are two key factors that control the diameter of carbon nanotubes. One is the control of catalyst particle size distribution, and the second is the control of CVD conditions. . First, the size distribution of the catalyst will directly affect the diameter distribution of carbon nanotubes. Zeolites, magnesium oxide, alumina, mesoporous silica, etc. can be used to synthesize nanoparticles with uniform and controllable sizes through solution chemistry methods, and can be used as catalysts or catalyst precursors to grow carbon nanotubes with controllable diameters. Using long-chain carboxylic acid or amine molecules as protective agents, or using apoferritin, dendrimers, block copolymers, etc. as nanoreactors can effectively control the size of nanoparticles and synthesize uniform carbon nanotube catalysts. Precursor. Catalyst supports can usually play a role in stabilizing the size of the catalyst and limiting catalyst agglomeration.

In the prior art, porous materials such as zeolite and mesoporous silica are commonly used as catalyst carriers. Although the porous structure plays a role in limiting the size of the catalyst, the zeolite and mesoporous silica carriers are difficult to remove, which poses challenges to the preparation and production of carbon nanotubes. The application brings some inconvenience.

Contents of the invention

Based on the above technical background, the inventors conducted intensive research and found that the catalyst precursor was prepared from a compound containing element A, a catalyst carrier and a complexing agent, and then the metal catalyst prepared by burning and reduction could be used for By growing bulk single-walled carbon nanotubes with small diameters, the single-walled carbon nanotubes produced have smaller diameters and a narrower diameter distribution.

The first aspect of the present invention is to provide a catalyst for the growth of small-diameter bulk single-walled carbon nanotubes. The catalyst is prepared from a compound containing element A, a catalyst carrier and a complexing agent. The element A is selected from iron. , one or more of cobalt, nickel, molybdenum, chromium, copper, tungsten, manganese, silver, gold, palladium, platinum, ruthenium, iridium, rhodium and rhenium.

The second aspect of the present invention is to provide a preparation method of the catalyst according to the first aspect of the present invention, which includes the following steps:

Step 1. Prepare a catalyst precursor using a compound containing element A, a catalyst carrier and a complexing agent;

Step 2: Prepare the catalyst through burning and reduction;

Element A is selected from one or more of iron, cobalt, nickel, molybdenum, chromium, copper, tungsten, manganese, silver, gold, palladium, platinum, ruthenium, iridium, rhodium, and rhenium;

The compound containing element A is selected from one or more water-soluble salts containing element A;

The catalyst carrier is selected from oxides of magnesium, aluminum, silicon, calcium, etc. or their mixed oxides, carbonates, various zeolites, boron nitride, etc.;

In particular, complexing agent molecules can coordinate the metal ions of element A, thereby inhibiting their hydrolysis and reducing their aggregation. Therefore, the prepared metal catalyst particles can be kept small and uniform in size, which is conducive to the growth of small-diameter single-walled carbon nanotubes;

The complexing agent is selected from one of ammonia, methylamine, pyridine, oxalate, o-phenanthroline, ethylenediamine, ethylenediaminetetraacetic acid or its salt, sodium tripolyphosphate, triethanolamine and sodium pyrophosphate, or Several kinds.

A third aspect of the present invention is to provide the use of a catalyst for the growth of small-diameter bulk single-walled carbon nanotubes prepared according to the catalyst of the first aspect of the present invention or prepared by the preparation method of the second aspect of the present invention, It can be used for the preparation of small-diameter bulk single-walled carbon nanotubes.

A fourth aspect of the present invention is to provide a method for preparing small-diameter bulk single-walled carbon nanotubes, which method includes the following steps:

Step a: Add catalyst to the tube furnace and raise the furnace temperature to the carbon nanotube growth temperature;

Step b: pass in a carbon source to prepare carbon nanotubes.

The invention provides a small-diameter bulk single-walled carbon nanotube growth catalyst and the small-diameter bulk single-walled carbon nanotubes prepared thereby have the following advantages: the catalyst carrier is simple to remove, facilitates the subsequent application of the carbon nanotubes, and has high preparation efficiency. , the carbon nanotubes produced have a smaller diameter and a narrower diameter distribution (diameter distribution is between 0.9 and 1.2nm), and are suitable for use in fields such as near-infrared biofluorescence imaging and quantum device single-photon light sources.

Description of the drawings

Figure 1 shows the Raman spectrum of the carbon nanotube laser wavelength 532nm prepared in Comparative Example 2 and Comparative Example 3 of the present invention;

Figure 2 shows the Raman spectrum of the carbon nanotube laser wavelength 633nm produced in Comparative Example 2 and Comparative Example 3 of the present invention;

Figure 3 shows the Raman spectrum of the carbon nanotube laser wavelength 532nm prepared in Comparative Example 2, Comparative Example 4 and Comparative Example 5 of the present invention;

Figure 4 shows the Raman spectrum of the carbon nanotube laser wavelength 633nm prepared in Comparative Example 2, Comparative Example 4 and Comparative Example 5 of the present invention;

Figure 5 shows the Raman spectra of carbon nanotube lasers with a wavelength of 532 nm prepared in Comparative Examples 2, 6, 7, 8, 9, 10, 11 and 12 of the present invention. picture;

Figure 6 shows the Raman spectra of carbon nanotube lasers with a wavelength of 633 nm prepared in Comparative Examples 2, 6, 7, 8, 9, 10, 11 and 12 of the present invention. picture;

Figure 7 shows the Raman spectra of carbon nanotube lasers with a wavelength of 532 nm prepared in Comparative Example 2, Comparative Example 13, Comparative Example 14, Comparative Example 15 and Comparative Example 16 of the present invention;

Figure 8 shows the Raman spectra of carbon nanotube lasers with a wavelength of 633 nm prepared in Comparative Example 2, Comparative Example 13, Comparative Example 14, Comparative Example 15 and Comparative Example 16 of the present invention;

Figure 9 shows the Raman spectrum of the carbon nanotube laser wavelength 532nm produced in Comparative Example 2 and Example 2 of the present invention;

Figure 10 shows the Raman spectra of carbon nanotubes produced in Comparative Example 2 and Example 2 of the present invention with a laser wavelength of 633 nm.

Detailed ways

The present invention will be described in detail below, and the features and advantages of the present invention will become clearer and clearer with these descriptions.

A first aspect of the present invention is to provide a catalyst for the growth of small-diameter bulk single-walled carbon nanotubes. The catalyst is prepared from a compound containing element A, a catalyst carrier and a complexing agent.

The compound containing element A is selected from one or more water-soluble salts containing element A, preferably one or more from the group consisting of sulfate, nitrate and acetate containing element A, More preferably, it is selected from sulfates containing element A.

Element A in the present invention is selected from one or more of iron, cobalt, nickel, molybdenum, chromium, copper, tungsten, manganese, silver, gold, palladium, platinum, ruthenium, iridium, rhodium and rhenium, preferably selected from One or more of iron, cobalt, nickel, copper, manganese and molybdenum, more preferably one or two of iron, cobalt and nickel.

The catalyst carrier is selected from one or more of magnesium oxide, alumina, silicon oxide, calcium oxide, magnesium carbonate, aluminum carbonate, silicon carbonate, calcium carbonate, zeolite and boron nitride, preferably selected from magnesium oxide, Y-type zeolite and one or more types of silicon oxide, more preferably magnesium oxide.

The molar ratio of the catalyst carrier to the compound containing element A is (30-70):1, preferably the molar ratio is (40-60):1, and more preferably the molar ratio is (45-55):1. When a bimetal is used in a compound containing A element, the molar ratio of the two metals is preferably 1:1.

The complexing agent is selected from one of ammonia, methylamine, pyridine, oxalate, o-phenanthroline, ethylenediamine, ethylenediaminetetraacetic acid or its salt, sodium tripolyphosphate, triethanolamine and sodium pyrophosphate, or Several, preferably one or more selected from oxalate, ethylenediaminetetraacetic acid or its salt and sodium tripolyphosphate, more preferably ethylenediaminetetraacetic acid or ethylenediaminetetraacetic acid sodium salt.

The added amount of the complexing agent is 1 to 15 times the molar amount of the compound containing element A (the molar amount in the present invention is the number of moles), preferably 2 to 10 times, more preferably 4 to 7 times, such as 5 times .

For preparing the catalyst according to the present invention, it is prepared by a method including the following steps:

Step 1. Prepare a catalyst precursor using a compound containing element A, a catalyst carrier and a complexing agent;

Step 2: Prepare the catalyst through burning and reduction.

A second aspect of the present invention is to provide a preparation method for the catalyst used for the growth of small-diameter bulk single-walled carbon nanotubes according to the first aspect of the present invention. The method includes the following steps:

Step 1. Prepare a catalyst precursor using a compound containing element A, a catalyst carrier and a complexing agent;

Step 2: Prepare the catalyst through burning and reduction;

This step is described and illustrated in detail below.

Step 1. Prepare a catalyst precursor using a compound containing element A, a catalyst carrier and a complexing agent.

The catalyst precursor is prepared by mixing a compound containing element A and a catalyst carrier and then post-processing. Before mixing, the compound containing element A and the catalyst carrier need to be dissolved in water and then mixed.

After the compound containing element A is dissolved in water, the molar concentration of element A is 0.1-1 mmol/mL, preferably the molar concentration is 0.1-0.5 mmol/mL, and more preferably the molar concentration is 0.1-0.2 mmol/mL.

The compound containing element A is selected from one or more water-soluble salts containing element A, preferably one or more from the group consisting of sulfate, nitrate and acetate containing element A, More preferably, it is selected from sulfates containing element A.

During the preparation process, the compound containing element A needs to be dissolved in water to make a solution and then mixed with the catalyst carrier. Therefore, the compound containing element A is a water-soluble salt, and the compound containing element A is soluble in water. Later, hydrolysis will occur during the later evaporation process. The more severe the degree of hydrolysis, the more serious the degree of agglomeration, the larger the size of the catalyst particles formed, resulting in an increase in the diameter of the carbon nanotubes, a lower degree of hydrolysis of sulfate, and the resulting carbon nanotubes. The tube diameter is smaller.

Element A in the present invention is selected from one or more of iron, cobalt, nickel, molybdenum, chromium, copper, tungsten, manganese, silver, gold, palladium, platinum, ruthenium, iridium, rhodium and rhenium, preferably selected from One or more of iron, cobalt, nickel, copper, manganese and molybdenum, more preferably one or two of iron, cobalt and nickel.

The inventor found that compared with a single metal catalyst, the use of a bimetallic catalyst system, such as a bimetallic catalyst system of iron and cobalt, can effectively improve the growth efficiency of carbon nanotubes while reducing the diameter and diameter of the carbon nanotubes. distributed.

The catalyst carrier is selected from one or more of magnesium oxide, alumina, silicon oxide, calcium oxide, magnesium carbonate, aluminum carbonate, silicon carbonate, calcium carbonate, zeolite and boron nitride, preferably selected from magnesium oxide, Y One or more of zeolite and silica, more preferably magnesium oxide.

Porous catalyst carriers can limit the size of the catalyst through nano-sized pores, thereby controlling the diameter of carbon nanotubes. However, porous structural carriers such as zeolites are difficult to remove, which brings certain inconveniences to the subsequent application of carbon nanotubes, and magnesium oxide As a catalyst carrier, it can be removed by soaking in dilute acid, which is very simple, and the diameter of the carbon nanotubes produced is smaller. At the same time, magnesium oxide can effectively control the size of iron and cobalt particles, making the diameter of the carbon nanotubes produced smaller. And the distribution is narrow.

The catalyst carrier is dispersed in water, and the concentration of the catalyst carrier is 0.05-1g/mL, preferably the concentration of the catalyst carrier is 0.07-0.5g/mL, and more preferably the concentration of the catalyst carrier is 0.1-0.2g/mL.

The molar ratio of the catalyst carrier to the compound containing element A is (30-70):1, preferably the molar ratio is (40-60):1, and more preferably the molar ratio is (45-55):1. When the catalyst is a bimetallic catalyst, the molar ratio of the two metals is preferably 1:1.

According to a preferred embodiment of the present invention, a complexing agent is also added during the preparation of the catalyst precursor. The inventor found that the added complexing agent can coordinate with metal ions such as iron and cobalt, thereby inhibiting their hydrolysis. , reducing its agglomeration and limiting the size of the catalyst particles, so that the prepared metal catalyst particles maintain a small and uniform size.

The complexing agent is selected from one of ammonia, methylamine, pyridine, oxalate, o-phenanthroline, ethylenediamine, ethylenediaminetetraacetic acid or its salt, sodium tripolyphosphate, triethanolamine and sodium pyrophosphate, or Several, preferably one or more selected from oxalate, ethylenediaminetetraacetic acid or its salt and sodium tripolyphosphate, more preferably ethylenediaminetetraacetic acid or ethylenediaminetetraacetic acid sodium salt.

The added amount of the complexing agent is 1 to 15 times the molar amount of the compound containing element A, preferably 2 to 10 times, and more preferably 4 to 7 times.

The compound containing element A and the catalyst carrier are preferably mixed under stirring, and the stirring time is preferably 5 to 20 minutes, more preferably 10 minutes.

After stirring, heat and boil. The boiling time is preferably 20 to 45 minutes, and the boiling time is more preferably 30 minutes. After cooling, post-processing is performed, which includes suction filtration, washing and drying.

The detergent is preferably water and ethanol, and the washing is performed multiple times, preferably 1 to 3 times each with water and 2 times with ethanol.

After washing, drying is carried out. The drying temperature is 100-150°C and the drying time is 10-15h. Preferably, the drying temperature is 110-130°C and the drying time is 11-13h. More preferably, the drying temperature The temperature is 120℃ and the drying time is 12h.

Step 2: Prepare the catalyst through burning and reduction.

The catalyst precursor prepared in step 1 is burned and reduced in sequence to obtain the catalyst. Both ignition and reduction take place in a tube furnace.

The burning is preferably carried out in an air atmosphere, the burning temperature is 400-1200°C, the burning temperature is preferably 600-800°C, and the burning temperature is more preferably 700°C.

The burning time is 1 to 60 minutes, preferably the burning time is 2 to 10 minutes, and the burning time is more preferably 3 minutes.

After burning, an inert gas is introduced into the tube furnace to discharge the air therein. The inert gas is preferably argon. The introduction rate of the inert gas is 100-300 sccm, preferably the introduction rate is 150-250 sccm, and more preferably The input rate is 200sccm.

The passing time is 2 to 15 minutes, preferably 3 to 10 minutes, more preferably 4 minutes.

The reduction is preferably carried out in a mixed atmosphere of inert gas and hydrogen, and the inert gas is preferably argon. The introduction rate of the inert gas is 50 to 200 sccm, preferably 70 to 150 sccm, and more preferably 100 sccm.

The hydrogen gas introduction rate is 20 to 100 sccm, preferably 40 to 70 sccm, and more preferably 50 sccm.

The reduction temperature is 500-1200°C, preferably the reduction temperature is 800-1000°C, and more preferably the reduction temperature is 900°C.

The reduction time is 1 to 60 minutes, preferably 2 to 5 minutes, and more preferably 3 minutes.

A third aspect of the present invention is to provide the use of a catalyst according to the first aspect of the present invention or a catalyst prepared by the preparation method of the second aspect of the present invention, which can be used for the production of small-diameter bulk single-walled carbon nanotubes. preparation.

A fourth aspect of the present invention is to provide a method for preparing small-diameter single-walled carbon nanotubes, which method includes the following steps:

Step a: Add a catalyst to the tube furnace and raise the furnace temperature to the carbon nanotube growth temperature.

The catalyst is the catalyst described in the first aspect of the present invention or the catalyst prepared according to the preparation method described in the second aspect of the present invention, and the prepared catalyst is placed in a tube furnace.

The temperature of the tube furnace is adjusted to the growth temperature of the carbon nanotubes, and the temperature adjustment process is performed under the protection of an inert gas, preferably under the protection of argon gas.

The passing amount of argon gas is 100 to 300 sccm, preferably the passing amount is 150 to 250 sccm, and more preferably the passing amount is 200 sccm.

The growth temperature of carbon nanotubes is 600-1000°C, preferably the growth temperature is 650-950°C, and more preferably the growth temperature is 700-900°C.

When the growth temperature of carbon nanotubes is lower than 600°C or higher than 1000°C, the growth efficiency of carbon nanotubes is significantly reduced. In the range of 600 to 1000°C, as the temperature gradually increases, the average diameter of carbon nanotubes gradually increases. big.

The growth time of carbon nanotubes is 5 to 30 minutes, and the preferred growth time is 10 to 25 minutes. More preferably, the growth time is 15 to 20 minutes.

Step b: pass in a carbon source to prepare carbon nanotubes.

In the present invention, the carbon source is selected from one or more of methanol, methane, carbon monoxide, ethanol, ethylene, acetylene, propanol, toluene and xylene, and is preferably selected from one or more of methanol, methane, carbon monoxide, ethanol and toluene. One or more species, more preferably one or more species selected from methane and ethanol, such as ethanol.

The type of carbon source has a great influence on the diameter of carbon nanotubes. Experiments have found that under the same conditions, the diameter of carbon nanotubes grown using ethanol as a carbon source is smaller than that of carbon nanotubes grown with other carbon sources.

In the present invention, the growth of carbon nanotubes also requires adding a mixture of inert gas and hydrogen, and the inert gas is preferably argon.

The feed rate of the inert gas is 100 to 300 sccm, preferably the feed rate is 150 to 250 sccm, and more preferably the feed rate is 200 sccm.

The hydrogen gas introduction rate is 10 to 50 sccm, preferably 20 to 40 sccm, and more preferably 30 sccm.

According to the present invention, when the carbon source is a gas, the carbon source is passed into the tube furnace together with the inert gas and hydrogen. When the carbon source is a liquid, the liquid carbon source is preferably placed in a bubbler, and the inert gas is bubbled through After the furnace is passed into the tube furnace, the inert gas serves as the carrier gas of the carbon source.

The ratio of the inert gas carrier gas feed rate of the liquid carbon source to the hydrogen gas feed rate is 200: (5-100), the preferred feed rate ratio is 200: (10-80), the more preferred feed rate The ratio is 200: (10~60).

The ratio of the carbon source and hydrogen feed rates also affects the diameter of the carbon nanotubes. As the carbon source and hydrogen feed ratio decreases, the diameter of the carbon nanotubes gradually decreases. When the feed ratio is too low, that is, When the hydrogen feed rate is too high, the growth of carbon nanotubes is inhibited. If the carbon source feed rate is too high, the graphitized carbon layer that grows will quickly cover the catalyst, blocking the catalyst from contacting new carbon source molecules, resulting in The catalyst is deactivated. Therefore, only a suitable feed rate ratio is beneficial to the growth and preparation of small-diameter carbon nanotubes.

The diameter of the small-diameter single-walled carbon nanotube is 0.9-1.2 nm. It is suitable for use in fields such as near-infrared biofluorescence imaging and quantum device single-photon light sources.

The beneficial effects of the present invention are:

(1) The small-diameter bulk single-walled carbon nanotube growth catalyst of the present invention uses a complexing agent during the preparation process. The catalyst can effectively limit the size of the catalyst particles, thereby realizing small-diameter bulk single-walled carbon nanotubes. growth;

(2) The method for removing the catalyst carrier in the small-diameter bulk single-walled carbon nanotube growth catalyst of the present invention is simple and can be removed by soaking with dilute acid, which facilitates the subsequent application of carbon nanotubes;

(3) The carbon nanotubes produced by the carbon nanotube preparation method of the present invention have a smaller diameter, ranging from 0.9 to 1.2 nm, and are suitable for use in fields such as near-infrared biofluorescence imaging and quantum device single-photon light sources.

Example

The present invention will be further described below through specific examples. These examples are only for illustrating the present invention and are not intended to limit the scope of the present invention.

Example 1 Preparation of Catalyst

Weigh 0.83mmolCo(SO ₄ ) ₂ ·7H ₂ O (purity 99.5%) and (NH ₄ ) ₂ Fe(SO ₄ ) ₂ ·6H ₂ O (purity 95%) respectively, and dissolve them in 7.0mL ultrapure water. , weigh 3.33g (83mmol) of light MgO into 33mL of ultrapure water, and sonicate for 5 minutes until evenly dispersed. Under stirring conditions, the Co(SO ₄ ) ₂ ·7H ₂ O solution and the (NH ₄ ) ₂ Fe(SO ₄ ) ₂ ·6H ₂ O solution were added dropwise to the MgO suspension (at this time the suspension The concentrations of Fe and Co in the solution are both 0.16 mol/L), then add EDTA (ethylenediaminetetraacetic acid) 5 times the sum of the molar amounts of Fe and Co, stir the suspension for 10 minutes, boil for 30 minutes, cool and pump Filter, wash twice with ultrapure water and absolute ethanol, and then dry in an oven at 120°C for 12 hours to obtain a FeCo/MgO catalyst with a molar ratio of Mg:Fe:Co=100:1:1. Precursor.

Weigh 50 mg of the catalyst precursor prepared above into a 7cm*0.5cm porcelain boat, push it into the center of the tube furnace, then heat it to 700°C for 3 minutes in an air atmosphere, and introduce Ar gas at 200 sccm for 4 minutes to discharge the tube. The air in the furnace was raised to 900°C at the same time. After rising to 900°C, 100 sccm of Ar gas and 50 sccm of H ₂ were introduced for 3 min, and the catalyst was obtained by reduction.

Example 2 Preparation of carbon nanotubes

The catalyst prepared in Example 1 was placed in a tube furnace, the furnace temperature was adjusted to 900°C under the protection of 200 sccm Ar gas, and 200 sccm Ar gas was passed through an ethanol (carbon source) bubbler (ice water bath constant temperature). Pour into the tube furnace and simultaneously add 30 sccm of H ₂ , keep it at 900°C for 15 minutes, and finally drop to room temperature under the protection of Ar gas and H ₂ atmosphere to obtain small-diameter single-walled carbon nanotubes.

Comparative ratio

Comparative example 1

Repeat the preparation process of Example 1, except that no ethylenediaminetetraacetic acid is added.

Comparative example 2

The preparation process of Example 2 was repeated, with the only difference being that the catalyst prepared in Comparative Example 1 was used.

Comparative example 3

Repeat the preparation process of Comparative Example 2, with the only difference being that methane is used as the carbon source, and while 200 sccm of Ar gas is introduced, CH ₄ 325 sccm and H ₂ 30 sccm are simultaneously introduced to prepare carbon nanotubes.

Comparative example 4

Repeat the preparation process of Comparative Example 2, the only difference is: weigh 0.83mmol Co(NO ₃ ) ₂ ·6H ₂ O (purity 98.5%) and Fe(NO ₃ ) ₃ ·9H ₂ O (purity 98.5%), and dissolve them in 7.0mL ultrapure water.

Comparative example 5

Repeat the preparation process of Comparative Example 2, the only difference is: weigh 0.83mmolCo(CH ₃ COO) ₂ ·4H ₂ O (purity 95%) and (NH ₄ ) ₂ Fe(SO ₄ ) ₂ ·6H ₂ O (purity 99.5 %), respectively dissolved in 7.0 mL ultrapure water.

Comparative example 6

Repeat the preparation process of Comparative Example 2, with the only difference being that 200 sccm of Ar gas is passed through an ethanol (carbon source) bubbler (ice-water bath constant temperature) and then introduced into the tube furnace, and at the same time, 80 sccm of H ₂ is introduced.

Comparative example 7

Repeat the preparation process of Comparative Example 2, with the only difference being that 200 sccm of Ar gas is passed through an ethanol (carbon source) bubbler (ice-water bath constant temperature) and then introduced into the tube furnace, and at the same time, 60 sccm of H ₂ is introduced.

Comparative example 8

Repeat the preparation process of Comparative Example 2, with the only difference being that 200 sccm of Ar gas is passed through an ethanol (carbon source) bubbler (ice-water bath constant temperature) and then introduced into the tube furnace, and at the same time, 50 sccm of H ₂ is introduced.

Comparative example 9

Repeat the preparation process of Comparative Example 2, with the only difference being that 200 sccm of Ar gas is passed through an ethanol (carbon source) bubbler (ice-water bath constant temperature) and then introduced into the tube furnace, and at the same time, 40 sccm of H ₂ is introduced.

Comparative example 10

Repeat the preparation process of Comparative Example 2, with the only difference being that 200 sccm of Ar gas is passed through an ethanol (carbon source) bubbler (ice-water bath constant temperature) and then introduced into the tube furnace, and at the same time, 20 sccm of H ₂ is introduced.

Comparative example 11

Repeat the preparation process of Comparative Example 2, with the only difference being that 200 sccm of Ar gas is passed through an ethanol (carbon source) bubbler (ice-water bath constant temperature) and then introduced into the tube furnace, and at the same time, 10 sccm of H ₂ is introduced.

Comparative example 12

Repeat the preparation process of Comparative Example 2, with the only difference being that 200 sccm of Ar gas is passed through an ethanol (carbon source) bubbler (ice-water bath constant temperature) and then introduced into the tubular furnace without hydrogen.

Comparative example 13

The preparation process of Comparative Example 2 was repeated, with the only difference being that the temperature for growing carbon nanotubes was 1000°C.

Comparative example 14

The preparation process of Comparative Example 2 was repeated, with the only difference being that the temperature for growing carbon nanotubes was 900°C.

Comparative example 15

The preparation process of Comparative Example 2 was repeated, with the only difference being that the temperature for growing carbon nanotubes was 800°C.

Comparative example 16

The preparation process of Comparative Example 2 was repeated, and the only difference was that the temperature for growing carbon nanotubes was 600°C.

Experimental example

Experimental Example 1 Raman Test

The carbon nanotubes prepared in Comparative Example 2 and Comparative Example 3 were tested using the LabRAM ARAMIS Raman spectrometer of Horiba Jobin-Yvon Company at laser wavelengths of 532nm and 633nm, respectively. The test spectrum of the laser wavelength of 532nm is as shown in the figure. 1, the test spectrum with a laser wavelength of 633nm is shown in Figure 2.

It can be seen from Figures 1 and 2 that the RBM peak position of carbon nanotubes grown with ethanol is significantly higher than that of carbon nanotubes grown with methane, indicating that the diameter of carbon nanotubes grown with methane is larger than that of carbon nanotubes grown with ethanol.

The carbon nanotubes prepared in Comparative Example 2, Comparative Example 4 and Comparative Example 5 were subjected to Raman tests at laser wavelengths of 532nm and 633nm respectively using Horiba Jobin-Yvon's LabRAM ARAMIS Raman spectrometer, and the laser wavelength was 532nm. The spectrum is shown in Figure 3, and the test spectrum with a laser wavelength of 633nm is shown in Figure 4.

It can be seen from Figure 3 and Figure 4 that the RBM peak of carbon nanotubes grown using sulfate precursor (prepared in Example 1) appears at a higher wave number, which means that the diameter of the carbon nanotubes is smaller. The carbon nanotubes grown on nitrate have the largest diameter.

The carbon nanometers prepared in Comparative Examples 2, 6, 7, 8, 9, 10, 11 and 12 were measured using Horiba Jobin-Yvon's LabRAM ARAMIS Raman spectrometer. The tubes were subjected to Raman testing at laser wavelengths of 532nm and 633nm respectively. The test spectrum of the laser wavelength of 532nm is shown in Figure 5, and the test spectrum of the laser wavelength of 633nm is shown in Figure 6.

It can be seen from Figure 5 and Figure 6 that as the hydrogen flow rate gradually increases from 0, the RBM peak of 100-180cm ^-1 in the Raman spectrum gradually weakens or disappears (corresponding to single-walled carbon nanoparticles with a diameter of 2.4-1.3nm). tube), while the RBM peak above 200cm ^-1 gradually increases (corresponding to single-walled carbon nanotubes with a diameter less than 1.2nm), indicating that as the carbon-to-hydrogen ratio decreases in the CVD atmosphere, the diameter of the grown carbon nanotubes gradually decreases. When the carbon-to-hydrogen ratio is too low, that is, when the hydrogen flow rate is too high, the RBM peak no longer appears in the Raman spectrum, and the growth of carbon nanotubes is inhibited.

The carbon nanotubes prepared in Comparative Example 2, Comparative Example 13, Comparative Example 14, Comparative Example 15 and Comparative Example 16 were used to perform Raman analysis at laser wavelengths of 532nm and 633nm respectively using the LabRAM ARAMIS Raman spectrometer of Horiba Jobin-Yvon Company. Test, the test spectrum with a laser wavelength of 532nm is shown in Figure 7, and the test spectrum with a laser wavelength of 633nm is shown in Figure 8.

In Figures 7 and 8, as the growth temperature of carbon nanotubes increases from 700°C to 900°C, the intensity of the lower wavenumber RBM peak in the Raman spectrum gradually increases, which means that as the temperature increases, the carbon nanotubes grow. The diameter of the tube gradually increases. When the growth temperature is 600°C and 1000°C, the growth efficiency of carbon nanotubes decreases significantly, and the RBM peak no longer appears in the Raman spectrum.

Using the LabRAM ARAMIS Raman spectrometer of Horiba Jobin-Yvon Company, the carbon nanotubes prepared in Comparative Example 2 and Example 2 were subjected to Raman tests at laser wavelengths of 532nm and 633nm respectively. The test spectrum of the laser wavelength of 532nm is as shown in the figure. 9, the test spectrum with a laser wavelength of 633 nm is shown in Figure 10.

It can be seen from Figures 9 and 10 that the RBM peak in the Raman spectrum of the carbon nanotubes prepared after adding EDTA is obviously blue-shifted, indicating that the diameter of the carbon nanotubes is reduced after adding EDTA, calculated from the RBM peak position (according to Zhang, D.; Yang, J.; Li, Y. Small, 2013, 9, 1284-1304.doi:10.1002/smll.201202986 calculated), the diameter of the carbon nanotubes grown after adding EDTA is in the range of 0.9~1.2nm Inside.

The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limitations of the present invention. Those skilled in the art understand that without departing from the spirit and scope of the invention, various equivalent substitutions, modifications or improvements can be made to the technical solution and its implementation of the invention, and these all fall within the scope of the invention. The scope of protection of the present invention is determined by the appended claims.

Claims (4)

1. A method for preparing small-diameter bulk single-walled carbon nanotubes, the method comprising the following steps: Step a: Add catalyst to the tube furnace and raise the furnace temperature to the carbon nanotube growth temperature; Step b: pass in a carbon source to prepare carbon nanotubes; The catalyst is prepared from a compound containing element A, a catalyst carrier and a complexing agent, and the element A is selected from one or more of iron, cobalt and nickel; The catalyst is prepared by a method including the following steps: Step 1. Prepare a catalyst precursor using a compound containing element A, a catalyst carrier and a complexing agent; Step 2: Prepare the catalyst through burning and reduction; In step 1, The compound containing element A is selected from one or more water-soluble salts containing element A; The catalyst carrier is magnesium oxide; The molar ratio of the catalyst carrier to the compound containing element A is (30-70): 1; The complexing agent is selected from ethylenediaminetetraacetic acid or its salt; The diameter of the small-diameter single-walled carbon nanotubes is 0.9-1.2 nm. 2. The method according to claim 1, wherein in step 1, the added amount of the complexing agent is 1 to 15 times the molar amount of the compound containing element A. 3. The method according to claim 1, wherein in step 2, The burning temperature is 400~1200℃, the burning atmosphere is air, and the burning time is 1~60min; The reduction temperature is 500 to 1200°C, the reduction atmosphere is a mixture of hydrogen and inert gas, and the reduction time is 1 to 60 minutes. 4. The preparation method according to claim 1, characterized in that, In step a, the growth temperature of the carbon nanotubes is 600-1000°C, and the growth time is 5-30 minutes; In step b, the carbon source is selected from one or more of methanol, methane, carbon monoxide, ethanol, ethylene, acetylene, propanol, toluene and xylene.